Dynamically Controlled Compressors

ABSTRACT

In systems comprising at least two compressors, the present invention provides an adequately sized vessel or tank in either or both the suction line or the discharge line of multiple compressors, in such a fashion that if the conditions of the first compressor change, it does not have an immediate effect on the other compressors, the vessel acting as a means of dampening the change.

FIELD OF THE INVENTION

The present invention relates to compressors. More specifically, the present invention is concerned with a dynamically controlled compressor system and method.

BACKGROUND OF THE INVENTION

As well known in the art, centrifugal compressors have an operating envelope, referred to as the compressor map, which is limited by a condition called choke and another condition called surge.

Current centrifugal compressors pump gas when operating within the surge and choke points. If a centrifugal compressor is left operating in a surge condition for any length of time, impellers thereof can overheat and damage the whole machine. Compressor manufacturers go to length at trying to protect the compressor from operating in these damaging conditions with a variety of surge detection devices, which, when they detect a surge, shut the machine down to prevent damage.

In order to conserve energy, some more recent centrifugal compressors have added speed control to increase its operating range and in these cases the compressors control system has become dynamic. While up until this point, the compressors were either on or off, they have thus become more intelligent and the dynamic nature of the controls causes the compressors to react to changes in the condition. In a most recent version now available on the marketplace, by the present applicant, the centrifugal compressors may have totally dynamic controls and continually optimizes their speed and the positions of their inlet guide vanes to maximize their efficiency. Up until this date, centrifugal compressors have been mainly single compressor systems, and in more recent years, when two compressors have been applied to the one machine, have run in parallel and the loading and unloading has been through the use of the (IGV) alone and have been controlled from the one controller and therefore load and unload at the same rate and at the same time.

Currently, compressors have a compressor map programmed into a control unit thereof, to adjust their speed and when necessary also operate their inlet guide vanes in order to maximize their performance. Such dynamic control system provides that the compressors adapt their operating parameters as the conditions in the system change and as the load in the system varies.

In the case of a system comprising one compressor, this dynamic control of the centrifugal compressor, whereby it actively changes its speed and inlet guide vane setting to optimize its performance at various operating conditions and capacity requirements, is handled by an own control logic of the compressor.

In systems comprising at least two compressors, as shown in FIG. 1 illustrating a first compressor comp 1 and a second compressor comp 2 in parallel between a low pressure side (suction line) and a high pressure side (discharge line), operating conditions of the first compressor may be directly effected by a change in pumping capacity of the second compressor. This may occur for example when one the compressors, a condenser or an evaporator, are not adequately sized and a pipe work to and from the compressors is not connected in an independent fashion, or in the case when multiple compressors are connected in parallel and the point of interconnection between the compressors is to a common point or a common pipe and the capacity at the connecting point is not adequate to compensate for the changes in the first compressor and therefore has an immediate effect on the second compressor.

With the event of these compressors having their own intelligence, there is now a need in the art for a centrifugal compressor system and method allowing a dynamic control of performance thereof over a wide operating range.

SUMMARY OF THE INVENTION

More specifically, there is provided a multiple compressor system, comprising at least a first and a second compressors in parallel between a low pressure side and a high pressure side; at least one inertia vessel connected to one of suction lines and discharge lines of the at least first and second compressors; wherein the at least one inertia vessel acts as a means of dampening changes of operation condition of the at least first and second compressors.

There is further provided a method for controlling a compressor system including at least two compressors arranged in parallel between a low pressure side and a high pressure side, comprising the step of connecting at least one inertia vessel to at least one of: a suction line and: a discharge line of at least one of the at least two compressors.

Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of embodiments thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1, labelled as Prior Art, illustrates a piping configuration of multiple compressors piped up in parallel, as known in the art;

FIG. 2 illustrates a system according to an embodiment of the present invention;

FIG. 3 illustrates a system according to an other embodiment of the present invention;

FIG. 4 illustrates a system according to a further embodiment of the present invention;

FIGS. 5 illustrate alternatives to the embodiment of FIG. 4;

FIG. 6 illustrates a system according to still a further embodiment of the present invention;

FIG. 7 illustrates an alternative to the embodiment of FIG. 6; and

FIG. 8 illustrates a system comprising multiple compressors piped in parallel to and from a common vessel, i.e. condenser and evaporator, which most likely does not require inertia tanks.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the case of a refrigeration system such as in air-conditioning unit for example, the load of the compressor varies as a function of time as well as the temperatures, and therefore pressures. These variations have impacts on the compressor operation and the compressor, in response, adjusts its speed and inlet guide vane.

Such a dynamic control system may be applied to conventional system using other types of positive displacement compressors such as reciprocating, scroll or screw compressors for example. In the case of an air compressor, the compressor may thus respond as the load demand changes in the process in which it is being applied, such as a manufacturing process.

In systems comprising at least two compressors, the present invention provides an adequately sized vessel or tank in either or both the suction line or the discharge line of multiple compressors, in such a fashion that if the conditions of the first compressor change, it does not have an immediate effect on the other compressors, the vessel acting as a means of dampening the change.

FIG. 2 illustrates a parallel piping system comprising a header arrangement to reduce the impact of a first compressor changes in operation on a second compressor: a common low pressure tank 12 is connected to the suction line and a high pressure tank 14 is connected to the discharge line of the compressors Comp 1 and Comp 2.

In the parallel piping system illustrated in FIG. 3, an expansion tank is installed in the discharge 14a, 14b and in the suction 12a, 12b lines of each compressors Comp 1 and Comp 2 to reduce the impact of the change in the first compressor operation on the second compressor.

FIG. 4 illustrates a system of hermetic or semi-hermetic compressors wherein a compressor housing, such as in a hermetic or semi-hermetic compressor, is provided, which is adequately sized to act as an inertia tank thus eliminating the need for external inertia tanks.

FIGS. 5 illustrate a system comprising two compressors sharing a same housing adequately sized to act as an inertia tank thus eliminating the need for an external inertia tank. This type of system may have one or more exit and entry ports (see FIGS. 5a and 5b).

FIG. 6 illustrates an alternative embodiment where a low and high pressure inertia tanks are provided, these inertia tanks being modular in design and connected by flanged connections or connections as provided by Victualic Inc. for example, the inlet and outlet pipes being connected at either end.

In FIG. 7, the inlet and outlet pipes to the inertia tanks may be connected into any part of the inertia tanks. When assembled in a modular way, the inlet and outlet connections may be installed into the middle of the stack in order to balance the distribution of the gas and reduce the size of the individual inertia tanks.

It is to be noted that refrigerant may enter and exit the system from any of at least one ports.

In a system as illustrated in FIG. 8, two compressors, a condenser and an evaporator, piped in parallel to a common condenser vessel 32 and from a common evaporator vessel 30, the condenser and the evaporator being adequately sized, are not generally required.

As people in the art will appreciate, the present invention may be used in applications where multiple dynamically controlled compressors are used to replace one large compressor and where the suction and discharge lines have to be connected to a heat exchanger through either or both the one entry and one exit points. An example of this would be a water chiller where there is one entry to the condenser and one exit from the evaporator. If the compressor only required one compressor, then there would be no problem, however where two or more compressors are needed to obtain a required capacity, then simply piping the compressors as is usually done in the art is inefficient. The connecting point of the pipe work needs to be of adequate size as to not have an immediate effect on the other compressors operating in the system.

The present invention may be applied to systems comprising more than two compressors. For example, the systems of FIGS. 2-8 may be expanded by adding additional compressors either when the systems are first installed or at a later date as required. Each of the systems may also have the capability to be piped up with single or multiple suction and discharge pipes.

Although the present invention has been described hereinabove by way of embodiments thereof, it may be modified, without departing from the nature and teachings of the subject invention as described herein. 

1. A multiple compressor system, comprising: at least two compressors in parallel between a low pressure side and a high pressure side; and at least one inertia vessel of a predetermined size connecting at least one of: i) suctions lines of the at least two compressors on the low pressure side and ii) discharge lines of the at least two compressors on the high pressure side; wherein said inertia vessel dampens operation fluctuations of the at least two compressors.
 2. The multiple compressor system according to claim 1, comprising a first inertia vessel of a predetermined size connecting the suctions lines of the at least two compressors on the low-pressure side and a second inertia vessel of a predetermined size connecting the discharge lines of the at least two compressors on the high-pressure side.
 3. The multiple compressor system according to claim 1, comprising a first inertia vessel of a predetermined size connecting the suctions lines of the at least two compressors on the low pressure side and a second inertia vessel of a predetermined size connecting the discharge lines of the at least two compressors on the high pressure side; wherein said first inertia vessel is formed of a vessel installed in the suction line of a first one of the compressors connected to a vessel installed in the suction line of a second one of the compressors, and said second inertia vessel is formed of a vessel installed in the discharge line of the first one of the compressors connected to a vessel installed in the discharge line of the second one of the compressors respectively.
 4. The multiple compressor system according to claim 1, wherein said at least first and second compressors are selected among hermetic and semi-hermetic compressors, said inertia vessel comprising a first housing of the first compressor connected to a second housing of the second compressor.
 5. The multiple compressor system according to claim 1, wherein said at least first and second compressors are contained in a common housing, said inertia vessel being formed by said common housing.
 6. The multiple compressor system according to claim 1, comprising a first inertia vessel connecting the suctions lines of the at least two compressors on the low pressure side and a second inertia vessel connecting the discharge lines of the at least two compressors on the high pressure side; wherein said first and second inertia vessels each are modular inertia vessels, whose respective size is adjustable.
 7. A method for controlling a compressor system including at least two compressors arranged in parallel between a low pressure side and a high pressure side, comprising the step of connecting at least one inertia vessel of a predetermined size to at least one of: i) suctions lines of the at least two compressors on the low pressure side and ii) discharge lines of the at least two compressors on the high pressure side; whereby the inertia vessel dampens operation fluctuations of the at least two compressors.
 8. The method of claim 7, comprising the step of connecting a first inertia vessel of a predetermined size to the suctions lines of the at least two compressors on the low-pressure side and a second inertia vessel of a predetermined size to the discharge lines of the at least two compressors on the high-pressure side.
 9. The method according to claim 7, comprising: installing a first inertia vessel of a predetermined size in the suction line of a first one of the compressors, installing a second inertia vessel of a predetermined size in the suction line of a second one of the compressors, and connecting said first and second inertia vessels on the low pressure side; installing a third inertia vessel of a predetermined size in the discharge line of the first one of the compressors, installing a fourth inertia vessel of a predetermined size in the discharge line of the second one of the compressors, and connecting said third and fourth inertia vessels.
 10. The method according to claim 7, comprising selecting the at least two compressors among hermetic and semi-hermetic compressors, said method comprising connecting a housing of a first one of the compressors to a housing of a second one of the compressors and connecting each housing in parallel between the low pressure side and the high pressure side.
 11. The method according to claim 7, the at least two compressors being contained in a common housing, said method comprising connecting the common housing to the low-pressure side and to the high-pressure side respectively.
 12. The method according to claim 7, comprising connecting a first modular inertia vessel to the suctions lines of the at least two compressors on the low pressure side and a second modular inertia vessel to the discharge lines of the at least two compressors on the high pressure side; whereby a respective size of the first and second modular inertia vessels is adjustable. 